1. Field
Embodiments of the present disclosure relate to an apparatus and method of estimating inductance of a permanent magnet synchronous motor (PMSM) which estimates parameters of the PMSM during sensorless operation.
2. Description of the Related Art
Most air conditioning apparatuses sold for home or industrial use employ electric motors to compress a refrigerant. Recently, a permanent magnet synchronous motor (PMSM) having excellent energy efficiency and output density has been proposed as an electric motor to drive a compressor in an air conditioning apparatus.
In order to effectively operate the PMSM, a vector control technique based on magnetic flux may be applied. Vector control has a high requirement of a position sensor to acquire a reference magnetic flux, but the position sensor has low reliability under the condition of a compressor which is sealed and raised to a high temperature and cost rise due to installation of the position sensor provides a burden to a manufacturer. Therefore, a sensorless control technique to drive a PMSM for compressors is widely applied. In order to implement sensorless control of a compressor, a sensorless technique using a voltage equation is generally used.
In the PMSM used in the compressor, designed values of parameters are present. However, the designed values differ from actual parameters due to environmental variation, i.e., change of natural phenomena which are relatively monotonously raised or lowered for a long time, manufacturing tolerance and operating environmental variation. In the sensorless technique using a voltage equation, parameters of the motor are used during a process of detecting the position of the magnetic flux of a rotor, and thus errors of the parameters of the motor used in sensorless control affect position estimation performance. That is, the errors in the parameters may lower control performance of the motor, and thus acquisition of correct parameters is important in sensorless operation.
The voltage equation used in sensorless operation is an equation between a d-axis coinciding with the magnetic flux of permanent magnets and a q-axis perpendicular to the d-axis. Therefore, in order to obtain parameters of the voltage equation, the position of the actual magnetic flux of the rotor needs to be first detected.
However, the position of the d-axis estimated through sensorless control under the condition that the correct parameters are not known, and position error of the d-axis is reflected in current error during d/q-axis conversion of phase current process and thus acts as error in estimating the parameters using the voltage equation.
Therefore, a measure to more accurately and reliably estimate parameters of a PMSM during sensorless operation may be required.